Book/Report

FZJ-2018-03893

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Genese und Expulsion von Kohlenwasserstoffen in zwei Regionen des Niedersächsischen Beckens unter besonderer Berücksichtigung der Aufheizraten

Düppenbecker, S. J. (Corresponding author)FZJ*

1992
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag Jülich

Please use a persistent id in citations: http://hdl.handle.net/2128/19213

Report No.: Juel-2657

Abstract: The effects of various geologic heating rates on the generation and expulsion of petroleum in two regions of the Lower Saxony Basin were studied using an integrated basin modelling approach and organic geochemical methods. The Lower Saxony Basin represents the most petroliferous region in Germany and the Posidonia Shale (Lower Toarcium, Jurassic) is the major prolific and regionally extensive source rock in this basin. In the Upper Cretaceous the thermal regime of the basin was strongly influenced by the intrusion of deep-seated igneous massives in the central and southern part. This thermal event caused different heating rates in various parts of the basin which had a significant effect on petroleum generation and expulsion. The two study areas were located in the western and southeastern part of the basin. Computer aided integrated basin modelling was applied in order to study generation and expulsion of petroleum with respect to thermal history. This included kinetic modelling of petroleum generation using specific parameters for Posidonia Shale. A new numerical model for petroleum expulsion was developed which considered mass and volume balancing of petroleum generation with changing petroleum composition and pressure/temperature conditions, fracturing of the source rock due to overpressure buildup and a pressure-driven petroleum phase flow through the pore network and newlyformed fractures. Core samples from well locations in the western and the southeastern regions of the basin have been investigated comprehensively by organic geochemical methods. The maturity of the Posidonia Shale ranges from 0.45% to 0.88% vitrinite reflectance and its organic facies is very homogeneous. Mass balance calculations of generated and expelled hydrocarbons in both regions show high expulsion efficiencies of more than 80% in mature source rock samples. The reconstructed temperature histories were calibrated by using organic geochemical maturity parameters and proved that a basin-wide thermal event at the beginning of the Upper Cretaceous influenced petroleum generation and expulsion of the Posidonia Shale in both regions. In the western region only moderate heating rates of less than 5°C/Ma were reconstructed and the process of petroleum generation and expulsion lasted about 8 Ma. In the southeastern region igneous intrusions caused much higher heating rates up to 25°C/Ma for a short period and the time of petroleum generation and expulsion was only half as long. As a consequence of high generation rates calculated pore pressure in the source rock exceeded the rock strength and expulsion was simulated along newlyformed microfractures. Such microfractures are present in mature Posidonia Shale cores of the southeastern region. In the western region lower generation rates resulted in reconstruction of petroleum expulsion through the pore network only and cores do not show any evidence for microfracturing. However, predicted expulsion efficiencies of 80%-90% for mature Posidonia Shale of both regions were not affected by the different heating rates. The results of this study indicate that the mechanism of petroleum expulsion is a functionof heating rates. The predicted influence of different heating rates on petroleum generation and expulsion were found to be qualitatively and quantitatively in goodagreement with present day geological and geochemical observations. In both regions migration and acccumuiation of petroleum expelled from the Posidonia Shale was reconstructed prior to and during the phase of basin inversion in Upper Cretaceous. Consequently present day oil accumulations in the western region are considered being in place since that time.

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Contributing Institute(s):

1. Publikationen vor 2000 (PRE-2000)

Research Program(s):

1. 899 - ohne Topic (POF3-899) (POF3-899)

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